<!DOCTYPE html>
<html>
 <head>
  <title>js基本包装类型</title>
  <meta charset="utf-8">
 </head>

 <body>
  <script>
   var s1 = 'hello world'
   console.log(s1.length)
   console.log(s1.constructor)

   console.log(s1.charAt(0))
   console.log(s1.charCodeAt(0))
   console.log('Mr '.concat('chen'))
  </script>
 </body>
</html>
